(1) Field of the Invention
The present invention is generally directed to the field of electronic servo mechanisms and more particularly to an improved arm assembly and a method for bonding a coil assembly to an actuator arm.
(2) Prior Art
Servo mechanisms for controlling the position of an arm, and for movement of the arm are known and used in a number of industries for performing a broad range of functions. The uses may include the movement and control of writing instruments such as pens, laser reading and writing elements. Other uses may include the movement of mechanical elements within electronic devices such as CD players, tape playing devices, etc. Miniaturization of components in the electronics industry has created the need for smaller and smaller servo mechanisms. In addition, many sectors of the electronics industry are moving towards portable battery powered systems. In these battery powered systems efficiency is extremely important as low power consumption is critical to battery life.
Though the servo mechanism described in the present invention could be used in any number of industries for any number of purposes, the servo mechanism will be described below with reference to it's use in the computer industry, and in particular with reference to a computer disk storage system.
In most disk storage systems a plurality of disks are stacked on a spindle and a corresponding plurality of magnetic heads are used to read to and/or write from the disk surfaces. The magnetic heads are typically mounted onto sliders which are suspended over the surfaces of the disk such that they fly over the surfaces of the disk upon the rotation of the disks. Each of the sliders is flexibly attached to an actuator arm. The actuator arm is mounted so that it can rotate about an axis such that the sliders may move across the radius of the spinning disk in order to provide access to all the surface area of the disk. Magnetic data is typically stored on the disk in a circular path, each circular path of stored data defining sectors located on the disk. The actuator arm is typically rotated by a magnetic motor drive. The magnetic motor drive consists of a pair of magnets suspended above and below a coil assembly consisting of wire wrapped around a bobbin which is mounted on to the arm assembly. The coil assembly is referred to in the computer industry as a "voice coil." Electrical current is applied to the voice coil so as to create a magnetic field. The interaction between this magnetic field and the magnetic field produced by the two magnets causes the actuator arm to rotate about a pivot pin. As the actuator arm is moved from one position to the another the read/write head traverses the radius of the surface of each disk. The platters and the actuator arm assembly are located in a chamber within the disk drive unit. The chamber protects the platters and the actuator arm assembly from dust and other particles that may become trapped within the drive case. These particles can render the disk drive inoperative if they would become entrenched into either the platters or the read/write heads and mechanisms.
Prior art arm assemblies typically contain an opening having a recessed ledge into which the voice coil is mounted. The ledges give a surface for attachment and with glue adhesive. The voice coil is typically attached to the actuator arm by placing both the voice coil and the actuator arm into a fixture. Glue is then applied to the entire perimeter of the interface between the voice coil and the actuator body. This glue is typically manually applied by an operator. The operator may apply too much or too little glue and the application is nonuniform. Some of the problems associated with this prior art method were the fact that the amount of glue applied along the bond line was totally reliant on the speed at which the operator moved along the perimeter interface. This results in an inconsistent amount of glue being applied along the bond line. Both the application of excessive glue and the application of insufficient glue are disadvantageous. The application of excessive glue can cause interference between the voice coil and the actuator arm and other devices such as the magnets which partially surround the voice coil and actuator arm. In addition, excessive glue can affect the balance of the arm. The application of insufficient glue may cause the voice coil to separate from the actuator arm body.
In order to avoid the problems associated with interference due to accessive glue application prior art methods have typically included a cleaning step. This cleaning step typically uses chemical cleaning solvents to remove any excess glue which protrudes above or below the voice coil and/or the arm. This additional cleaning step is undesirable as it adds an additional process stop which adds additional costs to the manufacturing process. In addition, an incomplete cleaning may create interface problems or smear glue over the surface of the coil so as to interfere with the effectiveness of the magnetic drive. Furthermore, fluorocarbons are typically used as cleaning solvents (CFC's, isopropyl alcohol, and acetone are also used.) These fluorocarbons are environmentally undesirable. Furthermore, the cleaning step may cause unwanted particles to adhere to the arm and the coil assembly and to be sealed within the chamber which houses the actuator arm and the disks. Another problem associated with the prior art methods include glue outgassing problems which may be compounded by the application of too much glue.
As disk drive units become smaller and smaller tolerances between the different component become more critical. Thus, the manufacture of components becomes more difficult. Thus, new methods for manufacture are required. Since, more and more disk drive units are being used on portable computers which have limited battery life, the efficiency issue becomes important. The efficiency of a magnetic drive motor is directly dependent on the distance between the actuator coil and the magnets. Prior arm systems typically employ a ledge assembly. The ledge assembly may shield a portion of the voice coil from the magnets, thereby reducing the magnetic flux produced by the voice coil. To avoid this problem, and to maintain the smallest possible distance between the voice coil and the magnets, smaller magnets are typically used. As the full flux of the voice coil cannot be used, and due to the reduced flux due to the use of smaller magnets which only partially cover the voice coil efficiency is reduced. Another problem associated with ledge structures is the fact that the ledge structures shield areas containing glue from the curing process such that curing may be complete or the cure stops requires more time to complete.
What is needed is a method for bonding a voice coil to an actuator arm which will not result in the over application or the under application of glue.